Overwintering Strategies Of Eurasian Red Squirrels (Sciurus Vulgairs) And Its Effects On Natural Regeneration Of Korean Pine

This paper made a scientific research on behavior ecology of Eurasian red squirrels' overwintering and its effect on natural regeneration of Korean pine in broad-leaved Korean pine mixed forest in Liangshui Nature Reserve since April 2007 to March 2009.Research contents included habitat selection,population distribution,hoarding-retrieving behavior,overwintering behavioral rhythm as well as home range use of Eurasian red squirrels.Based on"use-availability disproportion"hypothesis,the habitat preference of Eurasian red squirrels' nest-site was studied by transects method and locating observation.Data sets were analyzed by principal component analysis and Bailey' method.Results showed that(1)Eurasian red squirrels chose coniferous trees as nest trees which were higher and more approachable to surrounding trees.(2)Though Korean pine was the dominant species in study area,Eurasian red squirrels preferred fir and spruce as nest trees whose branches were more flourishing to Korean pine. Radio-tracing results also confirmed that Eurasian red squirrels used the nests on fir and spruce more frequently in winter.No matter whether the nest trees were in Korean pine forest or not,Eurasian red squirrels preferred to set nests in gap of Korean pine forest where fir and spruce were in dominance and the density and diversity of trees were higher than control samples.Fixed transects method was used to make a regular investigation of the distribution and dynamic of population of Eurasian squirrels in autumn and winter.Results demonstrated that Eurasian red squirrels distributed and overwintered not only in Korean pine forest,but also in nearby fir and spruce forest.The number of Eurasian red squirrels in Korean pine forest was 1-2 times as that in fir and spruce forest.The population density of Eurasian red squirrels in fir and spruce forest was more invariable than that in Korean pine forest.Seventy percent of Eurasian red squirrels in Korean pine forest were dead while overwintering mainly because of being preyed on. Alive-catching results manifested that sub-adults of Eurasian red squirrels with lighter body weight as subordinate individuals usually settled in fir and spruce forest as well as other various forests while the adults as dominant individuals dominated in Korean pine forest where they had quality source of food.However,radio-tracing results revealed that Eurasian red squirrels who settled out of Korean pine forest still entered Korean pine forest collected cones and then took them back home range during hoarding period.The hoarding behavior and cone selection of Eurasian red squirrels were studied according to series of methods and techniques,i.e.,located observation in certain study area,radio-tracing target animals methods,scanning samples in fixed transects,regular investigation on discarded cone cores in fixed transects.Results indicated that hoarding period of Eurasian red squirrels started in September and ended in November,lasting for 8-10 weeks.The beginning of hoarding was influenced by ripeness and pick(by other animals especially people)of pinecones.Eurasian red squirrels preferred to hoard bigger pinecones for high energy return.The process of hoarding can be sectioned into searching pinecones,processing pinecones,transporting a pinecone and hoarding seeds.Eurasian red squirrels peeled offscales ofpinecones whereafter held a pinecone in mouth and transported it towards a nest tree.Every pinecone was averagely taken to the base of 3 nest trees around which seeds were hoarded in batches.During each batch of hoarding the Eurasian red squirrel took about 8 seeds to construct 3-4 caches and finally 2-3 seeds were hoarded in each cache. Each Eurasian red squirrel averagely hoarded approximately 337 pinecones during the whole hoarding period in 2008.The number of hoarding pinecones by Eurasian red squirrels in Korean pine forest was almost 1 time higher than those who settled out of Korean pine forest.The hoarding habitat of Eurasian red squirrels was studied according to transects method and sample method.Result of principal component analysis pointed that several main factors affecting the selection of hoarding habitat of Eurasian red squirrels,such as distance to the Korean pine,forest type,the number of Korean pine seedlings,density and type of shrub.Selection of hoarding habitat of Eurasian red squirrels showed preference to forest where fir and spruce were in dominance.More than 50%of cone-cores were discarded within 300m along the edge and in the gap of Korean pine forest.This predicated that Eurasian red squirrels could take pinecones out of Korean pine forest. The distance of 150-600m to Korean pine forest showed no significance on the selection of hoarding habitat of Eurasian red squirrels corresponding with the radio-tracing results.The number of Korean pine seedlings in hoarding samples was notably lager than that in control samples.This indicated that hoarding habitat of Eurasian red squirrels was suitable for natural regeneration of Korean pine. Radio-tracing results manifested that Eurasian red squirrels might hoarding seeds at any moment while transporting pinecones.Within hoarded seeds by squirrels settled out of Korean pine forest, though 15%of them were hoarded out of home range,most of them were hoarded here and there within the range of 50m from nest trees.The density and canopy cover of arbors and shrubs in samples of nest trees were higher than that in areas of caches whose average diameter was about 40m.The behavioral rhythm and retrieving behavior of Eurasian red squirrels in winter was detected by radio-tracing target animals associating with investigating retrieving caches in certain area. Results revealed that the pattern of Eurasian red squirrels' activity was unimodal in winter.The delay of outgo time and decrease of activity while was notably accompanied with the decline of temperature.The home range of Eurasian red squirrels was similarly elliptical without overlaps, 2.55±0.04hm~2.There were several nests and cache-areas within each home range per Eurasian red squirrel.Every home range could be divided into 3 parts according to the position and use rate of nests and caches,i.e.,the major area,in mid-segment of the home range;2 minor areas,situated at ambo-sides of the major area.The hoarding seeds were main source of food for Eurasian red squirrels.One Eurasian red squirrel foraged 30.7±0.4 seeds per day,accumulating totally 4500 seeds during whole winter,approximately amounting to 45 pinecones.Eurasian red squirrels principally used caches in major area.The use rate among various caches was significantly different in each phase of winter.The rate of empty retrieve evidently increased as time went deep into winter. Consequently it was supposed that the spatial memory reminded Eurasian red squirrels of retrieving cached-seeds.Eurasian red squirrels alternatively used different nests in order to avoid being preyed on by predators.The use of nests remarkably related with the use of retrieving areas.Eurasian red squirrels usually stayed over in the nearest nest after retrieving so as to reduce energy consumption. It was deduced that multi-area retrieving based on scatter hoarding in certain aeras and the relevant tactics of nests alternation were integrated response to low temperature,cache pilferages and predators in winter.On the basis of the aforesaid results,Eurasian red squirrels made a contribution to natural regeneration of Korean pine in following aspects:1.Contribution to seed bank of Korean pine(1).Retrieving residuesThe number of cached-seeds was six to twelve times as that was consumed in harvest 2008, most of which wasn't eaten by Eurasian red squirrels in winter.(2).Hoarding bequestMany Eurasian red squirrels that died in winter bequeathed lots of hoarding sites of seeds.(3).Hoarding outside home rangeEurasian red squirrels hoarded part of seeds outside home range in winter no matter where they settled and how far from Korean pine forest.The aforementioned three sources of seeds would become part of the seed bank of natural regeneration of Korean pine if they escaped from the forage of other rodent animals.2.Determination of the dispersing range of seedsThe distribution of Eurasian red squirrels determined the dispersing range and direction of Korean pine seeds based on the directivity and region of hoarding behavior of Eurasian red squirrels.The hoarding density was highest in gap and coniferous forest 100-300m to Korean pine forest on population scale in accord with population distribution and home range structure of Eurasian red squirrels.The dispersing range of Korean pine seeds by Eurasian red squirrels included:gap and edge of Korean pine forest,inner and gap of natural coniferous forest as well as natural mixed coniferous and broad-leaved forest where Eurasian red squirrels settled.There is rarely direct relationship between regeneration of Korean pine in broad-leaved forest(especially younger broad-leaved forest)and Eurasian red squirrels' hoarding behavior.